The manufacture of circuit card assemblies includes the steps of soldering components to printed wiring boards and cleaning the boards of residue after soldering. Typically, an adhesive is applied to the larger electrical components, such as leaderless ceramic chip carriers, for the two-fold purpose of dampening vibrations and dissipating heat. If the completed circuit card assembly is inadequately cleaned during its manufacture, solder balls may remain near the leads of electrical components or corrosion may develop around the adhesive applied to the larger components. Solder balls can cause shorts between the leads and corrosion can cause long term reliability problems.
Corrosion is generally not a problem in commercial applications for computers since the environment in most commercial applications is relatively constant. Corrosion does become a problem in applications where the environment surrounding the computer will change, such as in military applications. Military applications are much more prone to introduction of moisture into the circuitry of a computer due to environmental changes. For example, a plane could be sitting on an aircraft carrier in 100.degree. F. heat and 99% humidity at one instance. Shortly after take-off the plane may be in an environment where it is -50.degree. F. As a result of this extreme temperature change, moisture can condense within an on-board computer. Once moisture is introduced into the computer or its components, corrosion becomes a real possibility. The fluxes used during the soldering process normally contain organic acids and activators containing halides. If the cleaning process is not exactly perfect, traces of the chlorine, florine or bromine will be left along with the cleaning fluid. When the moisture is introduced into such a system, corrosion may result.
To maximize the reliability of the completed circuit card assembly, engineers experiment with various cleaning processes and adhesive patterns so that solder balls are eliminated, and corrosion is eliminated or minimized. A cleaning process and an arrangement of adhesives are selected. The circuit card assembly is then manufactured using the selected process and adhesive arrangements. Presently, inspection for solder balls and corrosion is accomplished by removing the components from the circuit card assembly. One disadvantage of this method is the expense involved. Removing the components destroys the circuit card assembly and the components. Because of the expense involved with destroying circuit card assemblies, the number of experiments conducted are generally limited. Limiting the number of experiments, results in less chance that an optimum cleaning process and adhesive arrangement is found.
Another disadvantage is that the current method wastes time. In military contracting, one of the reliability standards requires that completed circuit card assemblies be placed in a humidity chamber for a period of ten days. In the humidity chamber, the environment cycles constantly between 90.degree. F. and 90% humdity and -10.degree. F. and 90% humidity. Presently completed circuit card assemblies are left in the humidity chamber for the full ten days, even though corrosion may have set in earlier. With a method of inspection where corrosion could be detected before the ten-day period, information about selected cleaning processes and adhesive arrangements could be obtained sooner so new selections could be made more quickly, thereby shortening the cycle time required to pick an optimal cleaning process and adhesive arrangement.
Consequently, there is a need for a method and apparatus by which the cleaning processes of the circuit card assembly and the positioning of the adhesives on the larger chips can be tested and inspected without destroying or ruining circuit card assemblies and the components on them. There is also a need for a method and apparatus in which corrosion in the circuit card assemblies can be detected prior to a ten-day cycle in the humidity chamber.